Random list of problems with i915g:

- What does this button do? Figure out LIS7 with regards to depth offset.

- Dies with BadDrawable on GLXFBconfig changes/destruction. Makes piglit totally
  unusable :( Upgrading xserver helped here, it doesn't crash anymore. Still
  broken, it doesn't update the viewport/get new buffers.

- Y-tiling is even more fun. i915c doesn't use it, maybe there's a reason?
  Texture sampling from Y-tiled buffers seems to work, though (save above
  problems).
  RESOLVED: Y-tiling works with the render engine, but not with the blitter.
  Use u_blitter and hw clears (PRIM3D_CLEAR_RECT).

- src/xvmc/i915_structs.h in xf86-video-intel has a few more bits of various
  commands defined. Scavenge them and see what's useful.

- Do smarter remapping. Right now we send everything onto tex coords 0-7.
  We could also use diffuse/specular and pack two sets of 2D coords in a single
  4D. Is it a big problem though? We're more limited by the # of texture
  indirections and the # of instructions.

- Finish front/back face. We need to add face support to lp_build_system_values_array and use it in draw_llvm.c.

- More optimizations, like replacing ADD + MUL with MAD or use DP2ADD.

- Replace constants and immediates which are 0,1,-1 or a combination of those with a swizzle.

- Schedule instructions to minimize the number of phases. One way is to replace
  R registers responsible for a boundary with U registers to avoid phase
  boundaries.

- Continue a previous primitive when there are no state changes

- Fix fragment discard

Other bugs can be found here:
https://gitlab.freedesktop.org/mesa/mesa/-/issues?scope=all&utf8=%E2%9C%93&state=opened&label_name[]=i915g
